This invention relates to a method of and an apparatus for controlling an idling control valve of an internal combustion engine, which method or apparatus can provide stable control of the idling control valve with relatively little electric current.
In an internal combustion engine for automobiles, etc., a target idle r.p.m. is determined with respect to an engine condition, such as engine temperature, in view of the level of purification of the exhaust gas, improvement in fuel consumption, etc., and such a technique is put into practice in such a way that real engine r.p.m. is caused to reach a target r.p.m. at a time of idling through feedback control. An example of the above-mentioned idle r.p.m. control is disclosed in Japanese Patent Publication No. 61-15257 (1986), wherein an idle control valve is disposed in a bypass passage bypassing a throttle portion of a suction passage, and current for driving the valve is changed with respect to engine temperature, such as engine cooling water temperature, thereby controlling the opening of the idle control valve followed by an idle air flow rate control. Some of these systems operate with the idle control valve kept opened to a predetermined opening at a time when the vehicle is under a condition of steady running. Another system is disclosed in Japanese Laid-Open No. 58-155239, wherein the opening of the idle control valve is increased temporarily when the engine is shifted from a steady running condition to a deceleration running condition whereby the vehicle can run smoothly during deceleration.
For the above-mentioned idle control systems, it is desirable to reduce an upper limit value of electric current for driving the valve to a value as little as possible in order to reduce electric power consumption and heat generation in the drive circuit in case the usual idle control valve control is effected.
For the idle control system in which the upper limit of the electric current is set to a small value, a movable part, such as the valve body, may stick to a supporting portion of the valve body when some substances, such as dust, adhere to the surfaces and the adhesion is heavy. In such a case, the valve body may not move even if electric current is supplied to the drive circuit because the electric current is restricted to the upper limit of the small value and is insufficient to move the valve body against the sticking force. Thus, in case the upper limit of the electric current to the drive circuit of the idle control value is set to a small value and some substances adhere to the surfaces, a stable operation of the idle control valve can not be expected.